Changing app.config as part of MSBuild script

I am using an MSBuild build file to build and test my application. As part of the process I would like to change the path and name of the log f开发者_C百科ile (setting in app.config). What is the easiest way to do it (I have the xpath to the value that needs to be changed)?

You can have a look at The MSBuild Community Tasks Project at http://msbuildtasks.tigris.org/ There's a task called XmlUpdate, which does exactly what you need.